Synthesis,COSMO-RS analysis and optical properties of surface modified ZnS quantum dots using ionic liquids

Zinc sulfide (ZnS) quantum dots (QDs) were synthesized using the microwave assisted ionic liquid (MAIL) route. Three ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄]), trihexyl(tetradecyl) phosphonium bis(trifluoromethanesulfonyl) amide ([P_6,6,6,14][TSFA]) and trihexyl(tetradecyl) phosphonium chloride ([P_6,6,6,14][Cl]) were used in this study. The size and structure of the QDs were characterized by high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern, respectively. The synthesized QDs were of wurtzite crystalline structure with size less than 5 nm. The QDs were more uniformly distributed while using the phosponium based ILs as a reaction medium during synthesis. The optical properties were investigated by UV–vis absorption and photoluminescence (PL) emission spectroscopy. The optical properties of QDs showed the quantum confinement effect in their absorption and the effect of cation and anion structural moiety was observed on their bandedge emission. The QDs emission intensity was measured higher for [P_6,6,6,14][Cl] due to their better dispersion as well as high charge density of Cl anion. The capability of the ILs in stabilizing the QDs was interpreted by density functional theory (DFT) computations. The obtained results are in good agreement with the theoretical prediction.     

Novel room temperature ionic liquid for fluorescence enhancement of Eu and Tb

The newly prepared ionic liquid, 1-butyl-3-methylimidazolium benzoate, ([bmim][BA]), was found to enhance the fluorescence of Eu³⁺ and Tb³⁺. The fluorescence enhancement resulted from a sensitization of the lanthanide fluorescence by the benzoate anion of the ionic liquid, [bmim][BA], and a reduction in the non-radiative channels in the non-aqueous environment provided by the ionic liquid. However, the fluorescence enhancement of the lanthanides in the ionic liquid was limited due to the operation of the inner filter effect, which resulted from the strong absorption of the benzoate. The inner filter effect was minimized by observing the Eu³⁺ fluorescence using a front face geometry and also by diluting the lanthanide-[bmim][BA] system, using another ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]), as a solvent. In the case of Tb³⁺, the emission from the lanthanide was masked by the strong emission from the ionic liquid in the region 450-580 nm. The long lived Tb³⁺ emission was therefore observed using delayed gated detection, where an appropriate delay was used to discriminate against the short lived emission from the ionic liquid. The large fluorescence enhancement due to ligand sensitized fluorescence observed with [bmim][BA] diluted in [bmim][Tf₂N], leads to nanomolar detection of the lanthanides. This is, to the best of our knowledge, the first report of an ionic liquid being employed for ligand sensitized fluorescence enhancement of lanthanides.     

Pressure-induced crystallization of 1-butyl-3-methylimidazolium hexafluorophosphate

We have investigated the pressure-induced crystallization of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) associated with the conformational changes of [bmim]⁺ by Raman spectroscopy. [bmim]⁺ has trans-trans and gauche-trans (GT) conformers of the butyl side chain at ambient pressure. Our result revealed that liquid to solid-phase transition occurs at 0.2–0.4 GPa region, where the GT conformer becomes dominant. We found that the GT dominant state continues up to 4 GPa.     

Ionic liquid; possibility of protein-preserving solvent under high pressure

We have investigated the pressure-induced phase transition behavior (～3.0 GPa) of aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions with N-methylacetamide (NMA), which is a simple protein model compound, using Raman spectroscopy. From Raman spectral changes and optical observation in the sequence of elevated pressure, we found that the aqueous [bmim][Cl] solution with NMA in the water-rich condition induces the high pressure crystallization at 2.6 GPa. On the other hand, in the [bmim][Cl]-rich condition, high pressure crystalline phase was not observed even up to 3.0 GPa. Our results show that the aqueous [bmim][Cl] solution in the ionic liquid-rich condition along with the use of pressure has a potential for protein-preserving solvent.     

Switching of hydrogen bonds of water in ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate

We have investigated temperature‐induced Raman spectral changes of deuterated water in an ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF₄]), between room temperature and 77 K. The comparison of the OH and OD stretching vibrational spectra at 77 K shows that the strength of the hydrogen bonds in [bmim][BF₄]–water mixtures strongly depends on the type of water, i.e. H₂O and D₂O. In the [bmim][BF₄]–D₂O system, remarkably strong hydrogen bonds form at low temperatures, but they switch to nearly free hydrogen bonds on heating. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface segregation in binary mixtures of imidazolium-based ionic liquids

Surface composition of binary mixtures of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry at room temperature over a wide composition range. The imidazolium cations with longer aliphatic groups tend to segregate to the surface, and a bis(trifluoromethanesulfonyl)imide anion (Tf₂N^?) is enriched at the surface relative to hexafluorophosphate (PF₆^?). The surface of an equimolar mixture of Li[Tf₂N] and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) has a nominal composition of [bmim][Tf₂N] because of surface segregation and ligand exchange. The surface segregation of cations and anions is likely to result from alignment of specific ligand-exchanged molecules at the topmost surface layer to exclude more hydrophobic part of the molecules.     

Templated electrodeposition of silver nanowires in a nanoporous polycarbonate membrane from a nonaqueous ionic liquid electrolyte

Template electrodeposition has been used to prepare a wide range of nanostructures but has generally been restricted to aqueous electrolytes. We report the deposition of silver nanowires in a commercial nuclear track-etched polycarbonate template from the nonaqueous ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) using silver electrochemically dissolved from the anode. Transmission electron microscopy (TEM) shows that the nanowires have a very high aspect ratio with an average diameter of 80 nm and length of 5 μm. Ionic liquid electrolytes should greatly extend the range of metals that can be electrodeposited as nanowires using templates. PACS 81.15.Pq; 81.07.-b     

Binary composite ionic liquids [bmim][BF4] and [bmim][Ac] for electrochemical reduction of nitrobenzene

The binary composite ionic liquid mixtures composed of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) and 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) were studied and used in electroreduction of nitrobenzene for the first time. ¹H NMR and Fourier transform infrared (FTIR) spectroscopy were carried out to acquire a deep understanding of the interaction of binary ionic liquids, and UV/Vis spectroscopy was used to study the interaction between the mixture of ionic liquids and nitrobenzene. It was found that chemical shifts of all protons were changed and significant changes in the anion IR bands were induced, and the UV maximum absorption wavelength and absorbance of nitrobenzene in binary ionic liquids were different from those in the neat ionic liquid. The electrochemical reduction behavior of nitrobenzene in binary composite ionic liquids on platinum electrode was studied by cyclic voltammetry, in situ Fourier transform infrared spectroscopy, and constant potential electrolysis. Results indicated that the reduction of nitrobenzene in binary composite ionic liquids demonstrated higher current densities with a more positive potential, and the product (azobenzene) showed higher yield and selectivity in the composite ionic liquids than in the neat ionic liquids; the concentrations of water in the binary mixtures of ionic liquids had great effect on the electrochemical behavior of nitrobenzene. In the end, the mechanism of reduction of nitrobenzene in binary mixtures of ionic liquids was discussed.     

An active nano-supported interface designed from gold nanoparticles embedded on ionic liquid for depositing DNA

The use of an active nano-interface designed from gold nanoparticles embedded on ionic liquid for DNA damage resulted from formalehyde (HCHO) is reported in this article. The active nano-interface was fabricated by depositing gold nanoparticles on the ionic liquid 1-butyl-3-methylimidazolium tetrafluroborate ([bmim][BF₄]). A glassy carbon electrode modified by this composite film was fabricated to immobilize DNA for probing into the damage resulted from HCHO. The modifying process was characterized by X-ray photoelectron spectroscopy, atomic force microscopy and electrochemistry involving electrochemical impedance spectroscopy. It was found that the modified film performs effectively in studying the DNA damage by electrocatalytic activity toward HCHO oxidation.     

离子液体阳离子在空气/[bmim][BF4]水溶液界面的取向和结构

采用和频振动光谱研究了空气/[bmim][BF₄]低浓度水溶液界面的取向结构. 研究发现,在体相浓度非常低时,丁基链具有较大的旁式扭曲,表明此时的取向比较无序;阳离子咪唑环则采取一个较小的取向角. 随着浓度的升高,阳离子咪唑环趋向平躺在界面. 由于链-链相互作用,此时丁基链的旁式扭曲也减小,说明界面分子的取向变得有序. 进一步研究发现,PPP和SPS光谱上甲基反对称的峰存在位移,表明界面丁基链上的甲基存在不同取向或具有不同的化学环境.结果有助于从微观层次理解水溶性离子液体和基于咪唑的表面活性剂在界面上的物理化学行为.     

Acoustic cavitation in 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide based ionic liquid

In this work, a comparison between the temperatures/pressures within acoustic cavitation bubble in an imidazolium-based room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide ([BMIM][NTf₂]), and in water has been made for a wide range of cavitation parameters including frequency (140–1000 kHz), acoustic intensity (0.5–1 W cm⁻²), liquid temperature (20–50 °C) and external static pressure (0.7–1.5 atm). The used cavitation model takes into account the liquid compressibility as well as the surface tension and the viscosity of the medium. It was found that the bubble temperatures and pressures were always much higher in the ionic liquid compared to those predicted in water. The valuable effect of [BMIM][NTf₂] on the bubble temperature was more pronounced at higher acoustic intensity and liquid temperature and lower frequency and external static pressure. However, confrontation between the predicted and the experimental estimated temperatures in ionic liquids showed an opposite trend as the temperatures measured in some pure ionic liquids are of the same order as those observed in water. The injection of liquid droplets into cavitation bubbles, the pyrolysis of ionic liquids at the bubble-solution interface as well as the lower number of collapsing bubbles in the ionic liquid may be the responsible for the lower measured bubble temperatures in ionic liquids, as compared with water.     

The electrochemistry of arylated anthraquinones in room temperature ionic liquids

Arylated anthraquinone derivatives of different sizes and different π‐basicities have been prepared, and the electrochemical behaviour of these substances has been studied on screen printed graphite electrodes in the three room temperature ionic liquids (RTILs), 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]), 1‐hexyl‐3‐methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) and 1‐octyl‐3‐methylimidazolium hexafluorophosphate ([C₈MIM][PF₆]). Half redox potentials for the first and second one electron reduction waves were identified, and the diffusion coefficient values were estimated from cyclic voltammetry measurements. The influence of the nature of the RTIL and of the substitution pattern of the anthraquinone on the solvodynamic radii were studied. A correlation of the reductive potentials with the corresponding Hammett constants of the substituents was tested. Copyright © 2013 John Wiley & Sons, Ltd.     

Ionic liquids in external electric and electromagnetic fields: a molecular dynamics study

The non-thermal effects of external electric and electromagnetic fields in the microwave to far-infrared frequency range and at (r.m.s.) electric field intensities of 10^?3 to 0.25?V/Å_r.m.s. on neat salts of 1,3-dimethyl-imidazolium hexafluorophosphate ([dmim][PF₆]) and 1-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF₆]) have been investigated by means of non-equilibrium molecular dynamics simulation. Significant alterations in molecular mobility were found vis-à-vis zero-field conditions. Using Green–Kubo and transient time correlation function analysis, the electrical conductivity of these ionic liquids has been estimated. The results indicate that ionic liquids respond most significantly to frequencies much lower than those of smaller polar solvents such as water, although the mechanism of the field response is almost exclusively translational.     

Surface structures of equimolar mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy

Surface structures of equimolar mixtures of imidazolium-based ionic liquids (ILs) having a common cation (1-butyl-3-methylimidazolium ([C₄MIM]) or 1-hexyl-3-methylimidazolium ([C₆MIM])) and different anions (bis(trifluoromethanesulfonyl)imide ([TFSI]), hexafluorophosphate ([PF₆]) or chlorine) are studied using high-resolution Rutherford backscattering spectroscopy (HRBS). Both cations and anions have the same preferential orientations at the surface as in the pure ILs. In the mixture, the larger anion is located shallower than the smaller anion. The [TFSI] anion is slightly enriched at the surface relative to [PF₆] with coverage of ~ 60% for the equimolar mixtures of [C₄₍₆₎MIM] [TFSI] and [C₄₍₆₎MIM] [PF₆]. No surface segregation is observed for [C₆MIM] [TFSI]_0.5[Cl]_0.5 and [C₆MIM] [PF₆]_0.5[Cl]_0.5. These results are different from the recent TOF-SIMS measurement where very strong surface segregation of [TFSI] was concluded for the mixture of [C₄MIM] [TFSI] and [C₄MIM] [PF₆].     

Measuring the solubility of benzoic acid in room temperature ionic liquids using chronoamperometric techniques

The electrochemical reduction of benzoic acid (BZA) has been studied at platinum micro‐electrodes (10 and 2 µm diameters) in acetonitrile (MeCN) and six room temperature ionic liquids (RTILs): [C₂mim][NTf₂], [C₄mim][NTf₂], [C₄mpyrr][NTf₂], [C₄mim][BF₄], [C₄mim][NO₃] and [C₄mim][PF₆] (where [C_nmim]⁺ = 1‐alkyl‐3‐methylimidazolium, [NTf₂]^? = bis(trifluoromethylsulphonyl)imide, [C₄mpyrr]⁺ = N‐butyl‐N‐methylpyrrolidinium, [BF₄]^? = tetrafluoroborate, [NO₃]^? = nitrate and [PF₆]^? = hexafluorophosphate). Based on the theoretical fitting to experimental chronoamperometric transients in [C₄mpyrr][NTf₂] and MeCN at several concentrations and on different size electrodes, it is suggested that a fast chemical step preceeds the electron transfer step in a CE mechanism (given below) in both RTILs and MeCN, leading to the appearance of a simple one‐electron transfer mechanism. The six RTIL solvents and MeCN were saturated with BZA, and potential‐step chronoamperometry revealed diffusion coefficients of 170, 4.6, 3.2, 2.7, 1.8, 0.26 and 0.96 × 10^?11 m² s^?1 and solubilities of 850, 75, 78, 74, 220, 2850 and 48 mM in MeCN and the six ionic liquids, respectively, at 298 K. The high solubility of BZA in [C₄mim][NO₃] may suggest a strong interaction of the dissolved proton with the nitrate anion. Although there are relatively few literature reports of solubilities of organic solutes in RTILs at present, these results suggest the need for further studies on the solubilities of organic species (particularly acids) in RTILs, because of the contrasting interaction of dissolved species with the RTIL ions. Chronoamperometry is suggested as a convenient methodology for this purpose. Copyright © 2008 John Wiley & Sons, Ltd.     

Ionic association and conductance of ionic liquids in dichloromethane at temperatures from 278.15 to 303.15 K

The electrical conductances of very dilute solutions of the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate [emim][BF₄] and 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF₄] in the low-permittivity solvent dichloromethane have been measured in the temperature range from 278.15 to 303.15 K at 5 K intervals. The data was analyzed assuming the possible presence of contact (CIP) and solvent-separated (SSIP) ion pairs in the solution on the basis of lcCM model to obtain ionic association constants, K _A, and the limiting molar conductivities, Λ_o, of these electrolytes. The examined ionic liquids are strongly associated in dichloromethane over the whole temperature range. From the temperature dependence of the limiting molar conductivities, the Eyring’s activation enthalpy of charge transport was determined. The thermodynamic functions such as Gibbs energy, entropy, and enthalpy of the process of ion pair formation were calculated from the temperature dependence of the association constants.     

An efficient enzymatic modification of cordycepin in ionic liquids under ultrasonic irradiation

A comparative study of the immobilized Candida antarctica lipase B (Novozym 435)-catalyzed acylation of cordycepin with vinyl acetate in ionic liquids (ILs) under ultrasonic irradiation and shaking was conducted. The application of ultrasonic irradiation instead of shaking during acylation resulted in an enhanced reaction rate and a higher level of substrate conversion. Among the various ILs examined, 1-butyl-3-methylimidazolium tetrafluorobrate ([C₄MIm][BF₄]) was the best medium for the reaction because it produced the highest substrate conversion. In [C₄MIm][BF₄], the optimal ultrasonic power, water activity, and reaction temperature were 120 W, 0.33, and 50 °C, respectively. The acylation of cordycepin in [C₄MIm][BF₄] proved to be regioselective under both conditions: the C5′-OH was acylated. Novozym 435 exhibited a much higher operational stability in [C₄MIm][BF₄], and 58.0% of its original activity was maintained after ten reuse cycles under ultrasonic irradiation. Compared with the cordycepin, the rate of adenosine deaminase-catalyzed deamination was greatly reduced when the 5′-OH was substituted by acetyl group. These results demonstrated that the combined application of ultrasonic irradiation and IL as a medium was an efficient approach for the enzymatic modification of cordycepin.     

Properties of Cellulose Regenerated from Powerful 1-Butyl-3-methylimidazolium Acetate/Dimethyl Sulfoxide Solvent

1-butyl-3-methylimidazolium?acetate C₄mim][CH₃COO]/dimethyl sulfoxide/DMSO can effectively dissolve cellulose at ambient temperature without any heating. However, the thermostability, morphology, and structure of cellulose regenerated from the [C₄mim][CH₃COO]/DMSO solvent is little known. Therefore, in this work, the regenerated cellulose was prepared and characterized by scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and the degree of polymerization (DP) measurements. The results indicated that the regenerated cellulose film displayed homogeneous structures; no chemical reaction occurred between cellulose and [C₄mim][CH₃COO] as well as DMSO during the dissolution and precipitation processes. The regenerated cellulose had good thermal stability, similar to the original cellulose, and the macromolecular chains of cellulose were hardly broken during the dissolution and precipitation processes.     

Volumetric, acoustic and spectroscopic studies for binary mixtures of ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) with alkoxyalkanols at T = (288.15 to 318.15) K

Densities and speeds of sound have been measured for the binary mixtures of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆] with ethylene glycol monoethyl ether (EGMEE), diethylene glycol monoethyl ether (Di-EGMEE), triethylene glycol monoethyl ether (Tri-EGMEE) over the whole composition range at atmospheric pressure. Experimental densities have been used to estimate excess molar volumes, V^E. Changes in isentropic compressibility, Δκ_s have been estimated by using experimental speed of sound and density values. Excess properties were fitted to the Redlich-Kister polynomial equation to obtain the binary coefficients and the standard errors. The molecular scale interactions between ionic liquid and alkoxyalkanols have been investigated through ¹H NMR spectroscopy. NMR chemical shifts for hydroxyl group of alkoxyalkanols and their deviations show hydrogen bonding interactions of varying strengths between ionic liquid and alkoxyalkanol in their binary mixtures.     

Synthesis and Optical Properties of 1-Alkyl-3-Methylimidazolium Lauryl Sulfate Ionic Liquids

We report the synthesis of a new series of imidazolium-based halogen-free ionic liquids 1-alkyl-3-methylimidazolium lauryl sulfates. By reacting 1-methylimidazole (MIM) with butyl, hexyl, octyl, and decyl bromides and exchanging bromide ion with lauryl sulfate anion, a series of ionic liquids [RMIM][C₁₂H₂₅OSO₃] were produced. The high purity of these ionic liquids was verified with ¹H-NMR, ¹³C-NMR, FT-IR and mass spectrometry (MS), demonstrating the effectiveness of this synthetic approach. Solubility test of these ionic liquids showed that they are soluble in most organic solvents except nonpolar solvents such as hexane and cyclohexane. The optical properties of [BMIM]Br and [BMIM][C₁₂H₂₅OSO₃], where B refers to butyl, were examined. Both ionic liquids absorbed light in the UV region, yet essentially no absorption was recorded beyond 450 nm. Furthermore, both ionic liquids showed excitation wavelength-dependent fluorescence behavior. As an example, with an excitation wavelength of 360 nm, [BMIM][C₁₂H₂₅OSO₃] showed an emission band maximum at 447 nm. Increasing the excitation wavelength to 440 nm, the emission band maximum was shifted to ∼500 nm.